IO-AIO/AIO.pm

=head1 NAME

IO::AIO - Asynchronous Input/Output

=head1 SYNOPSIS

 use IO::AIO;

 aio_open "/etc/passwd", O_RDONLY, 0, sub {
    my ($fh) = @_;
    ...
 };

 aio_unlink "/tmp/file", sub { };

 aio_read $fh, 30000, 1024, $buffer, 0, sub {
    $_[0] > 0 or die "read error: $!";
 };

 # Event
 Event->io (fd => IO::AIO::poll_fileno,
            poll => 'r',
            cb => \&IO::AIO::poll_cb);

 # Glib/Gtk2
 add_watch Glib::IO IO::AIO::poll_fileno,
           in => sub { IO::AIO::poll_cb; 1 };

 # Tk
 Tk::Event::IO->fileevent (IO::AIO::poll_fileno, "",
                           readable => \&IO::AIO::poll_cb);

 # Danga::Socket
 Danga::Socket->AddOtherFds (IO::AIO::poll_fileno =>
                             \&IO::AIO::poll_cb);


=head1 DESCRIPTION

This module implements asynchronous I/O using whatever means your
operating system supports.

Currently, a number of threads are started that execute your read/writes
and signal their completion. You don't need thread support in your libc or
perl, and the threads created by this module will not be visible to the
pthreads library. In the future, this module might make use of the native
aio functions available on many operating systems. However, they are often
not well-supported (Linux doesn't allow them on normal files currently,
for example), and they would only support aio_read and aio_write, so the
remaining functionality would have to be implemented using threads anyway.

Although the module will work with in the presence of other threads, it is
currently not reentrant, so use appropriate locking yourself, always call
C<poll_cb> from within the same thread, or never call C<poll_cb> (or other
C<aio_> functions) recursively.

=cut

package IO::AIO;

use base 'Exporter';

use Fcntl ();

BEGIN {
   $VERSION = 0.9;

   @EXPORT = qw(aio_read aio_write aio_open aio_close aio_stat aio_lstat aio_unlink
                aio_fsync aio_fdatasync aio_readahead);
   @EXPORT_OK = qw(poll_fileno poll_cb min_parallel max_parallel max_outstanding nreqs);

   require XSLoader;
   XSLoader::load IO::AIO, $VERSION;
}

=head1 FUNCTIONS

=head2 AIO FUNCTIONS

All the C<aio_*> calls are more or less thin wrappers around the syscall
with the same name (sans C<aio_>). The arguments are similar or identical,
and they all accept an additional (and optional) C<$callback> argument
which must be a code reference. This code reference will get called with
the syscall return code (e.g. most syscalls return C<-1> on error, unlike
perl, which usually delivers "false") as it's sole argument when the given
syscall has been executed asynchronously.

All functions that expect a filehandle will also accept a file descriptor.

The filenames you pass to these routines I<must> be absolute. The reason
for this is that at the time the request is being executed, the current
working directory could have changed. Alternatively, you can make sure
that you never change the current working directory.

=over 4

=item aio_open $pathname, $flags, $mode, $callback

Asynchronously open or create a file and call the callback with a newly
created filehandle for the file.

The pathname passed to C<aio_open> must be absolute. See API NOTES, above,
for an explanation.

The C<$flags> argument is a bitmask. See the C<Fcntl> module for a
list. They are the same as used by C<sysopen>.

Likewise, C<$mode> specifies the mode of the newly created file, if it
didn't exist and C<O_CREAT> has been given, just like perl's C<sysopen>,
except that it is mandatory (i.e. use C<0> if you don't create new files,
and C<0666> or C<0777> if you do).

Example:

   aio_open "/etc/passwd", O_RDONLY, 0, sub {
      if ($_[0]) {
         print "open successful, fh is $_[0]\n";
         ...
      } else {
         die "open failed: $!\n";
      }
   };

=item aio_close $fh, $callback

Asynchronously close a file and call the callback with the result
code. I<WARNING:> although accepted, you should not pass in a perl
filehandle here, as perl will likely close the file descriptor another
time when the filehandle is destroyed. Normally, you can safely call perls
C<close> or just let filehandles go out of scope.

This is supposed to be a bug in the API, so that might change. It's
therefore best to avoid this function.

=item aio_read  $fh,$offset,$length, $data,$dataoffset,$callback

=item aio_write $fh,$offset,$length, $data,$dataoffset,$callback

Reads or writes C<length> bytes from the specified C<fh> and C<offset>
into the scalar given by C<data> and offset C<dataoffset> and calls the
callback without the actual number of bytes read (or -1 on error, just
like the syscall).

Example: Read 15 bytes at offset 7 into scalar C<$buffer>, starting at
offset C<0> within the scalar:

   aio_read $fh, 7, 15, $buffer, 0, sub {
      $_[0] > 0 or die "read error: $!";
      print "read $_[0] bytes: <$buffer>\n";
   };

=item aio_readahead $fh,$offset,$length, $callback

Asynchronously reads the specified byte range into the page cache, using
the C<readahead> syscall. If that syscall doesn't exist (likely if your OS
isn't Linux) the status will be C<-1> and C<$!> is set to C<ENOSYS>.

C<aio_readahead> populates the page cache with data from a file so that
subsequent reads from that file will not block on disk I/O. The C<$offset>
argument specifies the starting point from which data is to be read and
C<$length> specifies the number of bytes to be read. I/O is performed in
whole pages, so that offset is effectively rounded down to a page boundary
and bytes are read up to the next page boundary greater than or equal to
(off-set+length). C<aio_readahead> does not read beyond the end of the
file. The current file offset of the file is left unchanged.

=item aio_stat  $fh_or_path, $callback

=item aio_lstat $fh, $callback

Works like perl's C<stat> or C<lstat> in void context. The callback will
be called after the stat and the results will be available using C<stat _>
or C<-s _> etc...

The pathname passed to C<aio_stat> must be absolute. See API NOTES, above,
for an explanation.

Currently, the stats are always 64-bit-stats, i.e. instead of returning an
error when stat'ing a large file, the results will be silently truncated
unless perl itself is compiled with large file support.

Example: Print the length of F</etc/passwd>:

   aio_stat "/etc/passwd", sub {
      $_[0] and die "stat failed: $!";
      print "size is ", -s _, "\n";
   };

=item aio_unlink $pathname, $callback

Asynchronously unlink (delete) a file and call the callback with the
result code.

=item aio_fsync $fh, $callback

Asynchronously call fsync on the given filehandle and call the callback
with the fsync result code.

=item aio_fdatasync $fh, $callback

Asynchronously call fdatasync on the given filehandle and call the
callback with the fdatasync result code. Might set C<$!> to C<ENOSYS> if
C<fdatasync> is not available.

=back

=head2 SUPPORT FUNCTIONS

=over 4

=item $fileno = IO::AIO::poll_fileno

Return the I<request result pipe file descriptor>. This filehandle must be
polled for reading by some mechanism outside this module (e.g. Event or
select, see below or the SYNOPSIS). If the pipe becomes readable you have
to call C<poll_cb> to check the results.

See C<poll_cb> for an example.

=item IO::AIO::poll_cb

Process all outstanding events on the result pipe. You have to call this
regularly. Returns the number of events processed. Returns immediately
when no events are outstanding.

Example: Install an Event watcher that automatically calls
IO::AIO::poll_cb with high priority:

   Event->io (fd => IO::AIO::poll_fileno,
              poll => 'r', async => 1,
              cb => \&IO::AIO::poll_cb);

=item IO::AIO::poll_wait

Wait till the result filehandle becomes ready for reading (simply does a
C<select> on the filehandle. This is useful if you want to synchronously wait
for some requests to finish).

See C<nreqs> for an example.

=item IO::AIO::nreqs

Returns the number of requests currently outstanding (i.e. for which their
callback has not been invoked yet).

Example: wait till there are no outstanding requests anymore:

   IO::AIO::poll_wait, IO::AIO::poll_cb
      while IO::AIO::nreqs;

=item IO::AIO::flush

Wait till all outstanding AIO requests have been handled.

Strictly equivalent to:

   IO::AIO::poll_wait, IO::AIO::poll_cb
      while IO::AIO::nreqs;

=item IO::AIO::poll

Waits until some requests have been handled.

Strictly equivalent to:

   IO::AIO::poll_wait, IO::AIO::poll_cb
      if IO::AIO::nreqs;

=item IO::AIO::min_parallel $nthreads

Set the minimum number of AIO threads to C<$nthreads>. The default is
C<1>, which means a single asynchronous operation can be done at one time
(the number of outstanding operations, however, is unlimited).

It is recommended to keep the number of threads low, as some Linux
kernel versions will scale negatively with the number of threads (higher
parallelity => MUCH higher latency). With current Linux 2.6 versions, 4-32
threads should be fine.

Under normal circumstances you don't need to call this function, as this
module automatically starts some threads (the exact number might change,
and is currently 4).

=item IO::AIO::max_parallel $nthreads

Sets the maximum number of AIO threads to C<$nthreads>. If more than
the specified number of threads are currently running, kill them. This
function blocks until the limit is reached.

This module automatically runs C<max_parallel 0> at program end, to ensure
that all threads are killed and that there are no outstanding requests.

Under normal circumstances you don't need to call this function.

=item $oldnreqs = IO::AIO::max_outstanding $nreqs

Sets the maximum number of outstanding requests to C<$nreqs>. If you
try to queue up more than this number of requests, the caller will block until
some requests have been handled.

The default is very large, so normally there is no practical limit. If you
queue up many requests in a loop it it often improves speed if you set
this to a relatively low number, such as C<100>.

Under normal circumstances you don't need to call this function.

=back

=cut

# support function to convert a fd into a perl filehandle
sub _fd2fh {
   return undef if $_[0] < 0;

   # try to be perl5.6-compatible
   local *AIO_FH;
   open AIO_FH, "+<&=$_[0]"
      or return undef;

   *AIO_FH
}

min_parallel 4;

END {
   max_parallel 0;
}

1;

=head1 SEE ALSO

L<Coro>, L<Linux::AIO>.

=head1 AUTHOR

 Marc Lehmann <schmorp@schmorp.de>
 http://home.schmorp.de/

=cut

Revision:	1.22
Committed:	Wed Jul 20 21:55:27 2005 UTC (18 years, 10 months ago) by root
Branch:	MAIN
CVS Tags:	rel-0_9
Changes since 1.21:	+4 -2 lines
Log Message:	* empty log message *
#	Content
1	=head1 NAME
2
3	IO::AIO - Asynchronous Input/Output
4
5	=head1 SYNOPSIS
6
7	use IO::AIO;
8
9	aio_open "/etc/passwd", O_RDONLY, 0, sub {
10	my ($fh) = @_;
11	...
12	};
13
14	aio_unlink "/tmp/file", sub { };
15
16	aio_read $fh, 30000, 1024, $buffer, 0, sub {
17	$_[0] > 0 or die "read error: $!";
18	};
19
20	# Event
21	Event->io (fd => IO::AIO::poll_fileno,
22	poll => 'r',
23	cb => \&IO::AIO::poll_cb);
24
25	# Glib/Gtk2
26	add_watch Glib::IO IO::AIO::poll_fileno,
27	in => sub { IO::AIO::poll_cb; 1 };
28
29	# Tk
30	Tk::Event::IO->fileevent (IO::AIO::poll_fileno, "",
31	readable => \&IO::AIO::poll_cb);
32
33	# Danga::Socket
34	Danga::Socket->AddOtherFds (IO::AIO::poll_fileno =>
35	\&IO::AIO::poll_cb);
36
37
38	=head1 DESCRIPTION
39
40	This module implements asynchronous I/O using whatever means your
41	operating system supports.
42
43	Currently, a number of threads are started that execute your read/writes
44	and signal their completion. You don't need thread support in your libc or
45	perl, and the threads created by this module will not be visible to the
46	pthreads library. In the future, this module might make use of the native
47	aio functions available on many operating systems. However, they are often
48	not well-supported (Linux doesn't allow them on normal files currently,
49	for example), and they would only support aio_read and aio_write, so the
50	remaining functionality would have to be implemented using threads anyway.
51
52	Although the module will work with in the presence of other threads, it is
53	currently not reentrant, so use appropriate locking yourself, always call
54	C<poll_cb> from within the same thread, or never call C<poll_cb> (or other
55	C<aio_> functions) recursively.
56
57	=cut
58
59	package IO::AIO;
60
61	use base 'Exporter';
62
63	use Fcntl ();
64
65	BEGIN {
66	$VERSION = 0.9;
67
68	@EXPORT = qw(aio_read aio_write aio_open aio_close aio_stat aio_lstat aio_unlink
69	aio_fsync aio_fdatasync aio_readahead);
70	@EXPORT_OK = qw(poll_fileno poll_cb min_parallel max_parallel max_outstanding nreqs);
71
72	require XSLoader;
73	XSLoader::load IO::AIO, $VERSION;
74	}
75
76	=head1 FUNCTIONS
77
78	=head2 AIO FUNCTIONS
79
80	All the C<aio_*> calls are more or less thin wrappers around the syscall
81	with the same name (sans C<aio_>). The arguments are similar or identical,
82	and they all accept an additional (and optional) C<$callback> argument
83	which must be a code reference. This code reference will get called with
84	the syscall return code (e.g. most syscalls return C<-1> on error, unlike
85	perl, which usually delivers "false") as it's sole argument when the given
86	syscall has been executed asynchronously.
87
88	All functions that expect a filehandle will also accept a file descriptor.
89
90	The filenames you pass to these routines I<must> be absolute. The reason
91	for this is that at the time the request is being executed, the current
92	working directory could have changed. Alternatively, you can make sure
93	that you never change the current working directory.
94
95	=over 4
96
97	=item aio_open $pathname, $flags, $mode, $callback
98
99	Asynchronously open or create a file and call the callback with a newly
100	created filehandle for the file.
101
102	The pathname passed to C<aio_open> must be absolute. See API NOTES, above,
103	for an explanation.
104
105	The C<$flags> argument is a bitmask. See the C<Fcntl> module for a
106	list. They are the same as used by C<sysopen>.
107
108	Likewise, C<$mode> specifies the mode of the newly created file, if it
109	didn't exist and C<O_CREAT> has been given, just like perl's C<sysopen>,
110	except that it is mandatory (i.e. use C<0> if you don't create new files,
111	and C<0666> or C<0777> if you do).
112
113	Example:
114
115	aio_open "/etc/passwd", O_RDONLY, 0, sub {
116	if ($_[0]) {
117	print "open successful, fh is $_[0]\n";
118	...
119	} else {
120	die "open failed: $!\n";
121	}
122	};
123
124	=item aio_close $fh, $callback
125
126	Asynchronously close a file and call the callback with the result
127	code. I<WARNING:> although accepted, you should not pass in a perl
128	filehandle here, as perl will likely close the file descriptor another
129	time when the filehandle is destroyed. Normally, you can safely call perls
130	C<close> or just let filehandles go out of scope.
131
132	This is supposed to be a bug in the API, so that might change. It's
133	therefore best to avoid this function.
134
135	=item aio_read $fh,$offset,$length, $data,$dataoffset,$callback
136
137	=item aio_write $fh,$offset,$length, $data,$dataoffset,$callback
138
139	Reads or writes C<length> bytes from the specified C<fh> and C<offset>
140	into the scalar given by C<data> and offset C<dataoffset> and calls the
141	callback without the actual number of bytes read (or -1 on error, just
142	like the syscall).
143
144	Example: Read 15 bytes at offset 7 into scalar C<$buffer>, starting at
145	offset C<0> within the scalar:
146
147	aio_read $fh, 7, 15, $buffer, 0, sub {
148	$_[0] > 0 or die "read error: $!";
149	print "read $_[0] bytes: <$buffer>\n";
150	};
151
152	=item aio_readahead $fh,$offset,$length, $callback
153
154	Asynchronously reads the specified byte range into the page cache, using
155	the C<readahead> syscall. If that syscall doesn't exist (likely if your OS
156	isn't Linux) the status will be C<-1> and C<$!> is set to C<ENOSYS>.
157
158	C<aio_readahead> populates the page cache with data from a file so that
159	subsequent reads from that file will not block on disk I/O. The C<$offset>
160	argument specifies the starting point from which data is to be read and
161	C<$length> specifies the number of bytes to be read. I/O is performed in
162	whole pages, so that offset is effectively rounded down to a page boundary
163	and bytes are read up to the next page boundary greater than or equal to
164	(off-set+length). C<aio_readahead> does not read beyond the end of the
165	file. The current file offset of the file is left unchanged.
166
167	=item aio_stat $fh_or_path, $callback
168
169	=item aio_lstat $fh, $callback
170
171	Works like perl's C<stat> or C<lstat> in void context. The callback will
172	be called after the stat and the results will be available using C<stat _>
173	or C<-s _> etc...
174
175	The pathname passed to C<aio_stat> must be absolute. See API NOTES, above,
176	for an explanation.
177
178	Currently, the stats are always 64-bit-stats, i.e. instead of returning an
179	error when stat'ing a large file, the results will be silently truncated
180	unless perl itself is compiled with large file support.
181
182	Example: Print the length of F</etc/passwd>:
183
184	aio_stat "/etc/passwd", sub {
185	$_[0] and die "stat failed: $!";
186	print "size is ", -s _, "\n";
187	};
188
189	=item aio_unlink $pathname, $callback
190
191	Asynchronously unlink (delete) a file and call the callback with the
192	result code.
193
194	=item aio_fsync $fh, $callback
195
196	Asynchronously call fsync on the given filehandle and call the callback
197	with the fsync result code.
198
199	=item aio_fdatasync $fh, $callback
200
201	Asynchronously call fdatasync on the given filehandle and call the
202	callback with the fdatasync result code. Might set C<$!> to C<ENOSYS> if
203	C<fdatasync> is not available.
204
205	=back
206
207	=head2 SUPPORT FUNCTIONS
208
209	=over 4
210
211	=item $fileno = IO::AIO::poll_fileno
212
213	Return the I<request result pipe file descriptor>. This filehandle must be
214	polled for reading by some mechanism outside this module (e.g. Event or
215	select, see below or the SYNOPSIS). If the pipe becomes readable you have
216	to call C<poll_cb> to check the results.
217
218	See C<poll_cb> for an example.
219
220	=item IO::AIO::poll_cb
221
222	Process all outstanding events on the result pipe. You have to call this
223	regularly. Returns the number of events processed. Returns immediately
224	when no events are outstanding.
225
226	Example: Install an Event watcher that automatically calls
227	IO::AIO::poll_cb with high priority:
228
229	Event->io (fd => IO::AIO::poll_fileno,
230	poll => 'r', async => 1,
231	cb => \&IO::AIO::poll_cb);
232
233	=item IO::AIO::poll_wait
234
235	Wait till the result filehandle becomes ready for reading (simply does a
236	C<select> on the filehandle. This is useful if you want to synchronously wait
237	for some requests to finish).
238
239	See C<nreqs> for an example.
240
241	=item IO::AIO::nreqs
242
243	Returns the number of requests currently outstanding (i.e. for which their
244	callback has not been invoked yet).
245
246	Example: wait till there are no outstanding requests anymore:
247
248	IO::AIO::poll_wait, IO::AIO::poll_cb
249	while IO::AIO::nreqs;
250
251	=item IO::AIO::flush
252
253	Wait till all outstanding AIO requests have been handled.
254
255	Strictly equivalent to:
256
257	IO::AIO::poll_wait, IO::AIO::poll_cb
258	while IO::AIO::nreqs;
259
260	=item IO::AIO::poll
261
262	Waits until some requests have been handled.
263
264	Strictly equivalent to:
265
266	IO::AIO::poll_wait, IO::AIO::poll_cb
267	if IO::AIO::nreqs;
268
269	=item IO::AIO::min_parallel $nthreads
270
271	Set the minimum number of AIO threads to C<$nthreads>. The default is
272	C<1>, which means a single asynchronous operation can be done at one time
273	(the number of outstanding operations, however, is unlimited).
274
275	It is recommended to keep the number of threads low, as some Linux
276	kernel versions will scale negatively with the number of threads (higher
277	parallelity => MUCH higher latency). With current Linux 2.6 versions, 4-32
278	threads should be fine.
279
280	Under normal circumstances you don't need to call this function, as this
281	module automatically starts some threads (the exact number might change,
282	and is currently 4).
283
284	=item IO::AIO::max_parallel $nthreads
285
286	Sets the maximum number of AIO threads to C<$nthreads>. If more than
287	the specified number of threads are currently running, kill them. This
288	function blocks until the limit is reached.
289
290	This module automatically runs C<max_parallel 0> at program end, to ensure
291	that all threads are killed and that there are no outstanding requests.
292
293	Under normal circumstances you don't need to call this function.
294
295	=item $oldnreqs = IO::AIO::max_outstanding $nreqs
296
297	Sets the maximum number of outstanding requests to C<$nreqs>. If you
298	try to queue up more than this number of requests, the caller will block until
299	some requests have been handled.
300
301	The default is very large, so normally there is no practical limit. If you
302	queue up many requests in a loop it it often improves speed if you set
303	this to a relatively low number, such as C<100>.
304
305	Under normal circumstances you don't need to call this function.
306
307	=back
308
309	=cut
310
311	# support function to convert a fd into a perl filehandle
312	sub _fd2fh {
313	return undef if $_[0] < 0;
314
315	# try to be perl5.6-compatible
316	local *AIO_FH;
317	open AIO_FH, "+<&=$_[0]"
318	or return undef;
319
320	*AIO_FH
321	}
322
323	min_parallel 4;
324
325	END {
326	max_parallel 0;
327	}
328
329	1;
330
331	=head1 SEE ALSO
332
333	L<Coro>, L<Linux::AIO>.
334
335	=head1 AUTHOR
336
337	Marc Lehmann <schmorp@schmorp.de>
338	http://home.schmorp.de/
339
340	=cut
341